It relates more particularly to improvements made to continuous-casting tundishes. These enclosures are metallurgical vessels coated with refractory materials enabling the liquid steel to be settled and then directed towards the continuous-casting moulds. Thus, conventional tundishes comprise an outlet zone bounded by dams, into which outlet zone the liquid steel is poured from a ladle. On each side of this outlet zone, the vessel includes a drain enabling the tundish to be drained towards the continuous-casting moulds. The dams act as a syphon so that the liquid steel is settled.
The continuous-casting mould is the place where steel passes from the liquid state to the solid state in the form of slabs, blooms or billets. The temperature at which the liquid steel enters the continuous-casting mould must be accurately regulated so that the liquid steel does not freeze either too soon or too late. This temperature depends on the treatments to which the liquid steel has been subjected upstream of the tundish; it has therefore hitherto been difficult to control.
Tundishes equipped with a plasma torch are thus known, this torch being designed to reheat the liquid steel in the tundish. Thus the purpose of the plasma heating is to increase and regulate the temperature of the liquid steel leaving the ladle, which, by mixing action, results in the temperature of the liquid steel in the tundish being maintained within a narrow and controlled band.
This type of tundish, therefore, comprises a heating chamber between the outlet zone and the distribution zone of the tundish. The heating chamber is separated from the outlet zone by means of dams so as, inter alia, to prevent the slag from passing through, which would limit the efficiency of the operation. The heating chamber is covered by a dome in order to prevent air ingress and reduce heat losses and oxidation of the liquid steel.
Furthermore, the liquid-steel outflow system, between the ladle-draining zone (outlet zone) and the plasma heating chamber, must be conducive to flow rates of the liquid steel which are sufficient to orient it under the impact of the arc of the plasma torch and must ensure effective stirring of the liquid-steel pool.
Tundishes not provided with a molten-steel reheat system do not produce steel in the continuous-casting mould at the desired solidification temperature, and for tundishes equipped with a reheating means consisting of a plasma torch the major drawback lies in the fact that the impact of the arc of the plasma torch is very localized at the surface of the steel pool, as is therefore the zone reheated by the arc. It is therefore important that the stream of steel coming from the outlet zone be directed precisely beneath the arc. Hitherto, the stream has been directed towards the arc by a plane dam which is inclined to a greater or lesser extent. These tundishes do not enable the stream to be directed as accurately as desired.